Although MIC Metering pressure transmitters use high-end sensors and electronic components and undergo strict environmental and indicator testing before leaving the factory, there are still many customers who encounter various problems during actual use, which are basically related to improper installation. The proper installation directly affects the accuracy, stability, and service life of its measurement. Here are some key points that need special attention during the installation process for your reference:

I.  Selection of pressure points

1. Representativeness: The pressure point must be able to truly reflect the process pressure to be measured. Avoid selecting areas near valves, elbows, throttling devices, container walls, or areas where the flow state of the medium is unstable (such as eddies, blind spots).

2. Consideration of medium characteristics:

Liquid: The pressure point should be on the side or bottom of the pipeline (to avoid gas accumulation), ensuring that the pipeline is filled with liquid. For horizontal pipelines, priority should be given to the side (to avoid blockage by sediment at the bottom).

Gas: The pressure point should be at the top or side of the pipeline (to avoid liquid accumulation). For horizontal pipelines, prioritize the top.

Steam: The pressure tapping point should be on the side of the pipeline, and a condenser/siphon should be installed to ensure that the pressure pipe is filled with condensed water and prevent high-temperature steam from directly impacting the transmitter diaphragm.

3. Accessibility: Easy to install, maintain, and calibrate.

II. Installation of pressure conduit

1. Pipe diameter and length: Seamless steel pipes with a diameter of 14 × 2 or 18 × 3 are usually used (or according to the requirements of the medium and specifications). The length should be as short as possible (generally not exceeding 50 meters) to reduce response lag and potential leakage points. Pipes that are too long or too thin will increase damping and affect dynamic response.

2. Slope:

Measuring liquids or vapors: The pressure pipe should be continuously inclined upwards (slope ≥ 1:10) from the pressure point to the transmitter to ensure that the gas inside the pipe can be smoothly discharged back into the process pipeline (liquid) or enter the condenser/collector (vapor), preventing the formation of gas plugs.

Measurement of gas: The pressure pipe should be continuously inclined downwards (slope ≥ 1:10) from the pressure point to the transmitter to ensure that the liquid inside the pipe can be smoothly discharged back into the process pipeline or enter the drain valve/collector, preventing the formation of liquid plugs.

3. Avoid U-shaped bends: It is strictly prohibited to form U-shaped or bag shaped bends on pressure pipes, as this can cause gas blockages (for measuring liquids/vapors) or liquid blockages (for measuring gases), resulting in measurement errors.

4. Bending radius: When bending, use a suitable pipe bender to avoid flattening or excessive deformation and ensure smooth inner diameter. The bending radius is usually not less than three times the diameter of the pipe.

5. Support and fixation: The pressure pipe should be firmly supported and fixed to prevent stress caused by vibration, thermal expansion and contraction, or external forces from being transmitted to the transmitter body or joint.

6. Discharge and exhaust: Install a discharge valve or exhaust valve at the lowest point (when measuring liquids/vapors) or highest point (when measuring gases) of the pressure pipe to facilitate discharge and exhaust operations and zero calibration of the pressure pipe.

7. Isolation and protection:

Corrosive/viscous/easily crystallizable media: Isolation tanks or diaphragm sealing systems (capillary tubes+remote flanges) must be used to protect the transmitter diaphragm with isolation fluid.

High temperature medium: It is necessary to use a condensing tank (steam) or a sufficiently long pressure pipe for natural cooling (liquid) to ensure that the temperature of the medium entering the transmitter is within its allowable range. It is strictly prohibited for high-temperature media to directly contact the transmitter diaphragm!

Pulsation/impact pressure: Install a pulse damper or buffer at the inlet of the transmitter.

Environmental protection: Exposed pressure pipes should consider insulation (anti freezing, anti scalding) or heat tracing (anti freezing, anti condensation), as well as protective measures to prevent mechanical damage.

III. Installation of transmitter body

1. Position and orientation:

Height: For differential pressure transmitters measuring liquids or vapors, the installation position should be lower than the pressure tapping point (to facilitate exhaust). For differential pressure transmitters used to measure gases, the installation position should be higher than the pressure point (to facilitate drainage). Pressure transmitters usually do not have such strict requirements, but the principle of pressure pipe slope still needs to be considered.

Direction: The process connection port (process flange/joint) on the transmitter body should be easy to access and maintain. Usually, electrical connection boxes (wiring chambers) should be installed facing downwards or horizontally to prevent rainwater, condensation, or dust from entering. Follow the manufacturer's recommendations for installation direction (some models have specific requirements).

2. Support and fixation:

Use sturdy mounting brackets or pipe racks to securely install the transmitter in a low vibration, easy to operate location (such as a wall, column, platform, or process pipeline).

Avoid stress: Ensure that no mechanical stress (torque, tension, lateral force) is applied to the process connection port (flange or thread) of the transmitter when connecting the pressure pipe to the transmitter. After connection, the transmitter body should be in a natural and stress free state. This is a common cause of zero drift and leakage! If necessary, use flexible joints or gooseneck tubes for transition.

3. Environmental conditions:

Temperature: The ambient temperature at the installation location should be within the operating temperature range of the transmitter. Avoid getting close to high-temperature heat sources (such as furnaces, steam pipelines) or direct sunlight. Ventilation or insulation measures should be considered for high temperature environments.

Vibration: Install in a location with minimal vibration as much as possible. If unavoidable, specialized shock-absorbing brackets or cushioning pads should be used.

Humidity and corrosion: Avoid installation in environments that are excessively humid or have corrosive gases or liquids splashing. Install protective covers if necessary.

Explosion proof: In explosive hazardous areas, installation, wiring, and grounding must be strictly carried out in accordance with explosion-proof requirements (such as explosion-proof and intrinsic safety), and certified explosion-proof sealing joints (gland heads) must be used.

IV. Electrical connection

1. Power supply and signal: Strictly follow the transmitter nameplate and wiring diagram for wiring (power and signal lines). Distinguish between two-line, three line, and four line systems. Pay attention to polarity.

2. Cable selection: Use cables that meet the specifications (wire diameter, shielding, insulation level). Use shielded cables in interference environments (such as near frequency converters).

3. Shielding and grounding:

Signal shielding layer: Single point grounding at the control system/safety barrier/power supply end (usually on the DCS/PLC cabinet side), suspended shielding layer at the transmitter end (not connected to the transmitter housing or on-site ground). Avoid grounding both ends to form a ground loop and introduce interference.

Grounding of transmitter housing: According to regulations and safety requirements, the metal housing of the transmitter usually needs to be connected to the instrument ground or protective ground (PE), using a yellow green grounding wire with sufficient cross-sectional area to connect to a reliable grounding terminal/grounding strip. This is a safety requirement, very important!

Intrinsic safety system: Grounding must be strictly carried out in accordance with the requirements of intrinsic safety systems (such as grounding of Zener safety barriers).

4. Wiring sealing: Cable entrances must use cable sealing joints (gland heads) that meet explosion-proof level (if applicable) and protection level (IP) requirements, tighten them, and ensure a waterproof and dustproof seal.

V.  Inspection and preparation before debugging

1. Valve status confirmation:

Ensure that the primary valve (root valve) and secondary valve (pressure pipe shut-off valve) are in the closed state.

The drain valve and exhaust valve are in the closed state.

2. Leakage inspection:

Before introducing the process medium, all joints, valves, and transmitter interfaces of the pressure pipe should be checked for airtightness/tightness (such as using soapy water to detect leaks) to ensure that there are no leaks. This is the key to safety!

3. Zero point calibration (preliminary): Before the installation is completed and the process medium is not introduced (the pressure tube is empty or filled with isolation liquid), under the premise of safety, the zero point output of the transmitter can be checked (considering the influence of differential pressure at the installation position), and if necessary, zero point migration can be performed (the migration amount is calculated based on the height difference of the capillary filling liquid or the installation position height difference).

4. Discharge/exhaust operation (first use):

Liquid/Steam:

Slowly open the valve once.

Slowly open the drain valve to remove air and impurities from the pipeline until the process medium (liquid) or condensed water (steam) continuously flows out, and then close the drain valve.

Slowly open the secondary valve (high pressure side and low pressure side).

Open the exhaust screw on the transmitter body (if any) or use an exhaust valve to completely exhaust the gas inside the transmitter measurement chamber until liquid flows out and tighten.

Gas:

Slowly open the valve once.

Slowly open the exhaust valve (or drain valve used as an exhaust valve) to discharge the liquid and impurities in the pipeline until there is continuous gas discharge, and then close the exhaust valve.

Slowly open the secondary valve (high pressure side and low pressure side).

Important! Operate the valve slowly to prevent pressure shock from damaging the transmitter diaphragm.

VI. Safety precautions

1. Energy isolation: Before installing, disassembling, maintaining transmitters or operating pressure pipe valves, it is necessary to strictly follow the LOTO procedure of the process system to isolate hazardous energy sources such as pressure sources, heat sources, and power sources.

2. Personal protective equipment: Wear appropriate PPE (safety helmet, protective goggles, gloves, protective clothing, etc.), especially when handling high temperature, high pressure, toxic, corrosive or flammable media.

3. Slowly operate the valve: When opening or closing any valve related to the pressure system, the action must be extremely slow to avoid pressure fluctuations (water hammer/steam hammer) damaging the transmitter diaphragm.

4. Pressure relief: Before disassembling the transmitter or disconnecting the pressure pipe, the pressure inside the pressure pipe must be completely relieved to a safe state through the drain valve/exhaust valve.

5. Medium hazards: Clearly understand the characteristics of the process medium (toxicity, corrosiveness, flammability and explosiveness, high temperature), and take corresponding protective measures.